Recently, an image displaying apparatus such as a liquid crystal display apparatus provided with a light source and a light modulating element, which modulates the intensity of the light from the light source, has been widely used. However, in the conventional image displaying apparatus, the light modulating element does not have ideal modulation characteristics; therefore, particularly when black is displayed, reduction in contrast caused by leakage of light from the light modulating element has occurred. Furthermore, since the light source is emitting light even when black is displayed, it has been difficult to reduce power consumption.
In order to suppress the reduction in contrast, a conventional technique in which luminance modulation of the light source and conversion of the gray levels of pixels of an input image (in other words, gamma conversion) are carried out in combination in accordance with the input image has been proposed. In all of the above described conventional techniques, the contrast can be increased by controlling the light-source luminance and the gray level conversion for the input image in accordance with the input image compared with an image displaying apparatus using constant light-source luminance. Moreover, since backlight luminance can be reduced in accordance with the input image, power consumption can be reduced.
However, when bright images are continuously displayed, the light source continues emitting light at high brightness. As a result, deterioration of the light source is advanced, the temperature of the light source is increased, and a problem that the life of the light source is shortened is caused.
In a plasma display panel (PDP) or an organic electro luminescence display (OLED), which is a light-emitting display apparatus having the problems similar to those described above, for example, still-image detection of input images is carried out; and, if a still image is continuously displayed for a predetermined period or longer, a process that, for example, reduces the contrast of the displayed image is carried out to prevent deterioration of a fluorescent body, which displays the image, (JP-A 2008-70683 (Kokai) and JP-A 2007-228474 (Kokai)).
The deterioration of the light source becomes a problem when a strong light emitting state continues for a long period of time. Therefore, in the conventional method in which the still images are detected, the luminance of the light source is reduced when a still image is continued for a certain period regardless of the light emitting state of the light source. Therefore, the luminance of the light source is excessively reduced, and image quality deterioration such as reduction in the screen luminance occurs.